Stephen Hawking believes that one of the major factors in the possible scarcity of intelligent life in our galaxy is the high probability of an asteroid or comet colliding with inhabited planets. We have observed, Hawking points out in Life in the Universe, the collision of a comet, Schumacher-Levi, with Jupiter (below), which produced a series of enormous fireballs, plumes many thousands of kilometers high, hot "bubbles" of gas in the atmosphere, and large dark "scars" on the atmosphere which had lifetimes on the order of weeks.

It is thought the collision of a rather smaller body with the Earth, about 70 million years ago, was responsible for the extinction of the dinosaurs. A few small early mammals survived, but anything as large as a human, would have almost certainly been wiped out.

Through Earth's history such collisions occur, on the average every one million year. If this figure is correct, it would mean that intelligent life on Earth has developed only because of the lucky chance that there have been no major collisions in the last 70 million years. Other planets in the galaxy, Hawking believes, on which life has developed, may not have had a long enough collision free period to evolve intelligent beings.

“The threat of the Earth being hit by an asteroid is increasingly being accepted as the single greatest natural disaster hazard faced by humanity,” according to Nick Bailey of the University of Southampton's School of Engineering Sciences team, who has developed a threat identifying program.[ Image: Comet Shoemaker-Levy 9 collision with Jupiter]

The team used raw data from multiple impact simulations to rank each country based on the number of times and how severely they would be affected by each impact. The software, called NEOimpactor (from NASA's "NEO" or Near Earth Object program), has been specifically developed for measuring the impact of 'small' asteroids under one kilometer in diameter.

Early results indicate that in terms of population lost, China, Indonesia, India, Japan and the United States face the greatest overall threat; while the United States, China, Sweden, Canada and Japan face the most severe economic effects due to the infrastructure destroyed.

The top ten countries most at risk are China, Indonesia, India, Japan, the United States, the Philippines, Italy, the United Kingdom, Brazil and Nigeria.

“The consequences for human populations and infrastructure as a result of an impact are enormous,” says Bailey. “Nearly one hundred years ago a remote region near the Tunguska River witnessed the largest asteroid impact event in living memory when a relatively small object (approximately 50 meters in diameter) exploded in mid-air. While it only flattened unpopulated forest, had it exploded over London it could have devastated everything within the M25. Our results highlight those countries that face the greatest risk from this most global of natural hazards and thus indicate which nations need to be involved in mitigating the threat.”

What would happen to the human species and life on Earth in general if an asteroid the size of the one that created the famous K/T Event of 65 million years ago at the end of the Mesozoic Era that resulted in the extinction of the dinosaurs impacted our planet.

As Stephen Hawking says, the general consensus is that any comet or asteroid greater than 20 kilometers in diameter that strikes the Earth will result in the complete annihilation of complex life - animals and higher plants. (The asteroid Vesta, for example, one of the destinations of the Dawn Mission, is the size of Arizona).

How many times in our galaxy alone has life finally evolved to the equivalent of our planets and animals on some far distant planet, only to be utterly destroyed by an impact? Galactic history suggests it might be a common occurrence.

The first this to understand about the KT event is that is was absolutely enormous: an asteroid (or comet) six to 10 miles in diameter streaked through the Earth's atmosphere at 25,000 miles an hour and struck the Yucatan region of Mexico with the force of 100 megatons -the equivalent of one Hiroshima bomb for every person alive on Earth today. Not a pretty scenario!

Recent calculations show that our planet would go into another "Snowball Earth" event like the one that occurred 600 million years ago, when it is believed the oceans froze over (although some scientists dispute this hypothesis -see link below).

While microbial bacteria might readily survive such calamitous impacts, our new understanding from the record of the Earth's mass extinctions clearly shows that plants and animals are very susceptible to extinction in the wake of an impact.

Impact rates depend on how many comets and asteroids exist in a particular planetary system. In general there is one major impact every million years -a mere blink of the eye in geological time. It also depends on how often those objects are perturbed from safe orbits that parallel the Earth's orbit to new, Earth-crossing orbits that might, sooner or later, result in a catastrophic K/T or Permian-type mass extinction.

The asteroid that hit Vredefort located in the Free State Province of South Africa is one of the largest to ever impact Earth, estimated at over 10 km (6 miles) wide, although it is believed by many that the original size of the impact structure could have been 250 km in diameter, or possibly larger(though the Wilkes Land crater in Antarctica, if confirmed to have been the result of an impact event, is even larger at 500 kilometers across). The town of Vredefort is situated in the crater (image).

Dating back 2,023 million years, it is the oldest astrobleme found on earth so far, with a radius of 190km, it is also the most deeply eroded. Vredefort Dome Vredefort bears witness to the world’s greatest known single energy release event, which caused devastating global change, including, according to many scientists, major evolutionary changes.

What has kept the Earth "safe" at least the past 65 million years, other than blind luck is the massive gravitational field of Jupiter, our cosmic guardian, with its stable circular orbit far from the sun, which assures a low number of impacts resulting in mass extinctions by sweeping up and scatters away most of the dangerous Earth-orbit-crossing comets and asteroids

Posted by Casey Kazan with Rebecca Sato

Note: This post was adapted from a news release issued by University of Southampton.

Comments

I have read this same topic churned over and over so many times that I cannot remember how many times . Yet every answer is always the same and that is look to the government . I believe that is not the answer . Here is a post that I put on the blog.nss.org
"I really like this blog with the links and all . However the glass half empty guys that post here are really something else . With the billions made , saved by the use of space . Even lives on earth have been saved through weather fax , communication , etc. We have built the second space colony in space #1 skylab # 2 iss . Either one was a failed colony as was james town . We now stand as it were firmly on the far shore that is space . There is unlimited energy ,unlimited resources unlimited space for us to grow and grow even more wealth then is possible here on the good earth. The lure of all of this is not going to be ignored or unexploited as it is not now .Space tech companies are publicly traded every week day and they for the most part not effected by the “great recession ” If one does as I have done invest in space tech companies . Put YOUR money where the whining comes out you will not only help to build the platforms to the stars but you will make money because money will come and go in and out of nasa but the final frontier isn’t going any where . If you need proof then check you gps …… is it still working. " This blog could be a tool for the advancement to further the goal of saving us or some of us by putting our collective heads to find the best of breed to invest our money in and we as a collective have much more money than any and all governments . Instead of watching the sky in fear . Give us a list of all the publicly traded companies that are actually doing something other then waiting for the inevitable and lets put our money and shoulders to the wheel of life .

The fossil record shows otherwise, does it not? Doesn't the theory of punctuated equilibrium lie on the periodic mass extinctions the planet goes through? The greatest evolutionary leaps are always post-extinction. It seems more likely that these mass extinctions have sped up evolution rather than to hinder it.

The odds are with us, since it is likely that within a century it will be rather easy to spot asteroids and nudge them into safe trajectories. A100 years is 1% of 1% of one million years -- PDQ, if you ask me.

That "average" of 1 impact per million years also says nothing about the distribution of the impacts in time, which shows a large bulge followed by a very long, thin, tail. The average in the last billion years, e.g., is a small fraction of that figure.

"What would happen to the human species and life on Earth in general if an asteroid the size of the one that created the famous K/T Event of 65 million years ago at the end of the Mesozoic Era that resulted in the extinction of the dinosaurs impacted our planet."

The article seems to suggest that an asteroid like the one that wiped out the dinosaurs normally hits once every million years. suppose the chances were 50 50 each million years. The chance of getting through 65 million years without an asteroid or comet of the size that doomed the dinosaurs is 2 to the 65 power. About one over a number 100 million times the high estimate for the number of stars in our galaxy, the Milky Way.

Of course asteroids that big do not hit the earth every million years or the dinosaurs would not have lasted as long as they did.

Many species of mammals survived the impact of the dinosaur extinction asteroid. Yes, a warm blooded animal our size would almost undoubtedly be wiped out, but it is very unlikely that we would be wiped out. Dinosaurs did not have mines, submarines, large stores of food, and radios to find members of the opposite sex from a great distance. Most of us might well die, but the human race would easily survive an impact like the one that took out the dinosaurs.

This is all very interesting, but remember there are billions of things going on out there that we can't even imagine that could destroy out Earth. Granted asteroids are common, but have you given any thought to aliens taking us out? I'm not an atheist, I believe in God, and I am not a Bible thumper. But I read a very interesting story of how we destroy 2/3 of the Earth and 2/3 of its population. And then Jesus comes down and rules and lives with man for the next thousand years in peace. That Jesus is probably an alien (we need ruling by a super intelligent alien because we are so violent and destructive we can't manage ourselves or this lovely Earth). Now before you dismiss this idea, there are many paintings (and other art pieces) of the holy family with a saucer shaped aircraft in the sky in the painting.

This is really a piece of shit article. I know this has already been said, but I'm just really appalled at what you guys try to pass off as science and the quality of writing you're willing to print. Typos everywhere, sentence fragments, misleading statistics.. you should really be ashamed of yourselves.

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It seems to me that asteroid collisions are an obstacle only to developing intelligent life, but not sustaining it. Once developed, intelligent life would prevent its planet from being hit by asteroids.

Seemingly there should be planets out there that have lucked into 60-70 million years of no asteroids, developed intelligent life and are now free from worrying about asteroid collisions. Whether something else has killed them off is for another article.

The fossil record shows otherwise, does it not? Doesn't the theory of punctuated equilibrium lie on the periodic mass extinctions the planet goes through? The greatest evolutionary leaps are always post-extinction. It seems more likely that these mass extinctions have sped up evolution rather than to hinder it.

Thanks for the article. Its a funny thing, the randomness of the universe. A big asteroid could just come and have its way with us (unless of course Bruce Willis has something to say about it :) )
Its an interesting point about other potential civilizations wiped out, whereas we have had the sheer dumb luck to have survived.

. Asteroid impacts can be caused by stray rubble from the Asteroid Belt and the rocky snowballs that travel in highly elliptical orbits in the comet cloud. There are many fewer large bits of debris than small bits, so the interval between large impacts is much longer than the interval between small impacts.